The Amazing Story of Printed Circuit Boards

Printed circuit boards, or PCBs, are used in billions of devices today and are manufactured by many companies. These companies offer various custom PCB solutions including rigid PCBs, rigid-flex PCBs, and flexible PCBs.  Just how are these made? PCBs connect electronic parts along etched paths on a copper background that has been laminated to a non-conducting surface. The copper foil layer acts as a conducting surface and is insulated with the non-conducting layer using epoxy resin. These non-conducting layers are brightly colored, the most common being green, but you may also see blue, red and black layers. These layers are typically made of cotton paper or woven glass and epoxy. Since cotton can expand and contract with heat, woven glass is considered the more stable insulating layer compound.

The circuit board starts out as a blank sheet of copper foil, sometimes with copper on two sides, with laminated backing. Whether the PCB will be mass manufactured or used for only a few models dictates how the paths or pattern will be imprinted on the copper. If there will be a large amount of PCB's needed, then they will be printed using a subtractive process like a silk screen, photographic or milling method. A PCB can also be produced using an additive process if it is a double-sided board.

Silk screen printing places protective inks on the copper that causes copper to remain on the board after it has been placed through an etching process. If any unwanted copper remains, it is etched again. In some cases, the manufacturer will use conductive ink printed on a non-conducive board that has no copper foil. Photoengraving employs a photographic sheet and develops it to reveal anything not protected by a photo-resistant coating. The copper is protected by the coating. Laser printing and laser imaging produce the photographic sheet. Milling uses x, y and z coordinates to control milling heads that physically rub away the copper. The milling heads are automated using a computer driven by PCB programs.

Additive processes are used with boards that have multiple layers and must be drilled as this process enables copper plating of holes. For this method, the blank insulated board has a thin layer of copper which is unmasked in the places where more copper is needed. More copper is added to these areas.

After the board is printed, it is then put through the etching process to expose the desired amount of copper. Many manufacturers use a spray etching which uses nozzles to spray ferric chloride or ammonium persulfate over the boards. A pump circulates the chemicals, and the nozzle pattern, temperature and flow rate can be controlled. The dissolved copper can then be recycled for profit.

After etching, the boards are then rinsed and prepared for plating so that components can be added. The exposed copper is covered with solder or other metals, such as nickel and gold. The copper is usually treated or plated because copper oxidizes and will resist the soldering of the new components. New solder compounds without harmful lead are now being used due to new RoHS directives, so the new solder is now 99.3% tin as opposed to the old tin-lead mixture.

Once the board has been plated, it is then subject to a test to ensure that the circuit connections are correct. A computer will administer a needle with voltage to the contact points on the board. Another test uses 3D scanning of the board which shows the soldering grids and connections.

Once the board becomes a true PCB, it’s ready for the components. If there are holes, then the components are inserted through these. If the board is using surface mount construction, then the parts are mounted to the board using hot solder. High-volume manufacturing uses an SMT placement machine, bulk soldering or even ovens. In some cases, technicians must be used to hand solder extremely tiny parts.

Once the parts have been added, the PCB is tested one more time by visual testing, analog signature testing, for voltage and frequency and for functionality.

It’s wonderful that so many electronic gadgets have been made available to consumers at affordable prices. And it’s amazing that this has been made possible considering all the steps involved in making a PCB. PCB solutions can be found easily by searching the Internet.

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